U.S. Secretary of Defense Jim Mattis says he has signed orders to deploy additional American troops to Afghanistan beyond the 11,000 currently serving in the war-torn country.

Speaking to reporters Thursday at the Pentagon, Mattis said the additional troops would mostly advise and "enable the Afghan forces to fight more effectively" against the Taliban and more than a dozen terror groups in Afghanistan.

The secretary said he would provide the public with more information once he had completed the orders and notified Congress next week of the military's next steps.

"I've signed orders, but it's not complete. In other words, I've signed some of the troops that will go and we're identifying the specific ones," Mattis said.

A U.S. Marine takes part during a training session for Afghan army commandos in Shorab military camp in Helmand province, Afghanistan, Aug. 27, 2017.

News of the new deployment orders comes a day after the Pentagon announced that approximately 11,000 U.S. troops are currently serving in Afghanistan, not 8,400 troops, as the Defense Department had previously reported.

The higher number emerged following Mattis's call for a more accurate troop-strength estimate, as the Trump administration worked on a new U.S. policy in Afghanistan.

The chief spokesperson at the Pentagon, Dana White, told reporters Wednesday the estimate of 11,000 troops is based on a simplified accounting method that provides greater "transparency" while "increasing commanders' ability to adapt to battlefield conditions."

The lower number of troops cited previously excluded service members on assignment in Afghanistan for less than 120 days — short-term duty that could include temporary combat support or materiel recovery missions.

Lieutenant General Kenneth "Frank" McKenzie Jr., staff director on the Joint Chiefs of Staff, said the new method of counting troops in the field uses approximations rather than exact numbers of troops. This, he said, allows commanders "more flexibility" when it comes to battlefield deployments.

"We all recognize that whole units are inherently more prepared and more ready than units that are fragmented in order to meet an arbitrary force management level," McKenzie said.

White and McKenzie said the changes made in calculating troop strength in Afghanistan eventually will be applied to American troops fighting the Islamic State group in Iraq and Syria.

Officials have suggested that Secretary Mattis is looking to deploy about 4,000 additional troops to Afghanistan to fulfill the commander's needs on the ground.